Measurement Method and System for Navigation Signal and Online

Diagnosis Method and System for Navigation Equipment

Yujun Bai

1, a

, Ping Yang

2, b, *

, Jing Liu

2, c

, Jiaquan Ye

2, d

, Zhengbo Yang

2, e

and Fei Liang

2, f

East China Regional Air Traffic Management Bureau CAAC, Shanghai, 200335, China

The Second Research Institute of CAAC, Chengdu 610041, China

yangzhengbo@caacsri.com,

liangfei@caacsri.com

Keywords: Navigation measurement equipment, Diagnosis, instrument landing system, Fast Fourier transformation,

Method of moment, Physical optics, Electromagnetic propagation theory.

Abstract: Due to the influence of the surrounding environment of airport’s navigation equipment, the existing

measurement technology cannot carry out fault diagnosis of navigation equipment according to the results

of the measurement system of the navigation equipment, and the staff can only carry out artificial fault

diagnosis according to their experience. However, the artificial diagnosis results may be inaccurate. This

paper proposes a navigation signal measurement method and system, in order to eliminate or reduce the

environmental factors interference to the measurement, so that the navigation equipment test system can

measures the navigation signal more accurately, and obtains more accurate measurement results. Based on

the measurement results, this paper also proposes an online diagnosis method and system for navigation

equipment, which can realize the online diagnosis of navigation equipment and has a high accuracy.

1 INTRODUCTION

Civil aviation navigation equipment is very

important to ensuring aviation flight safety,

measuring the equipment is now highly regarded at

home and abroad. International Civil Aviation

Organization (ICAO), International Radio

Consultative Committee (CCIR) and the

International Special Committee on Radio

Interference (CISPR) and other international

organizations have developed and issued related

documents of navigation equipment, that include

inspection and maintenance methods of navigation

equipment. The Civil Aviation Administration of

China (CAAC) also has developed relevant measure

procedures, requirements and flight inspection

criterion of aviation equipment (

S. Bo and W. Yong,

2011; E. Ma, J. Li, B. Liu and P. Wang, 2010

When the airport navigation system works, the

working condition and navigation accuracy of the

navigation equipment are closely related to the fault

of the navigation equipment itself and the

surrounding environment, such as buildings,

navigation equipment sites, radio interference and

other factors. Navigation equipment uses space

signals to guide aircraft, the characteristics of space

signals are not only related to the navigation

equipment itself, but also affected by the

environment around the station (

J. Chen, S. Zheng and

J. Liu, 2011

). When an object is located in the

protected area of the site, it will reflect the signal of

the navigation equipment and change the signal

radiation environment. Under the influence of

environmental factors around navigation equipment,

navigation test equipment will produce measurement

errors, leading to uncertainty measurement results.

During the measurement of navigation test

equipment, due to the influence of personnel

operation and surrounding environment, errors may

be inconsistent during on-site calibration, so the

errors caused by various factors need to be analysed

(

G. Li, H. Wei and S. Sun, 2011; B. Wang, P. Yang, J. Liu,

et al, 2017). At present, the test equipment at home

and abroad is regularly calibrated, and the possible

errors are corrected by embedding self-test modules

in the test equipment, but the influence caused by

non-equipment factors in the test site is not

considered.

For the measurement results of navigation test

equipment, the future development trend is: fully

considering the impact of the test site environment

on the measurement results, correct the measurement

274

Yang, P., Bai, Y., Liu, J., Ye, J., Yang, Z. and Liang, F.

Measurement Method and System for Navigation Signal and Online Diagnosis Method and System for Navigation Equipment.

DOI: 10.5220/0008378902740279

In Proceedings of 5th International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2019), pages 274-279

ISBN: 978-989-758-412-1

results and comprehensive judge the fault of

navigation equipment based on the corrected

measurement results, and give relevant suggestions.

At present, only foreign R&S companies have

started to introduce fault diagnosis system, which

can preliminarily analyse the fault reasons of

navigation equipment, and mainly judge based on

domestic experience.

2 A MEASUREMENT METHOD

AND SYSTEM FOR

NAVIGATION SIGNAL, AND

AN ONLINE DIAGNOSIS

METHOD AND SYSTEM FOR

NAVIGATION EQUIPMENT

In order to solve the existing technical problems,

when analysing the measurement results, it is

necessary to fully consider the impact of factors of

the navigation equipment itself, environmental

factors and personnel operation on the measurement

results, so that the measurement results can truly

reflect the state of the navigation equipment during

testing. The measurement uncertainty of navigation

online test system needs to consider various factors

such as the signal radiation of navigation equipment

and the reflection of measurement equipment on the

signal, and it needs to combine various methods

such as electromagnetic signal simulation and

experimental verification to obtain more accurate

uncertainty factors.

In view of the defects in the existing technology,

this paper proposes a navigation signal measurement

method and system, in order to eliminate or reduce

the interference of environmental factors on the

measurement, so that the navigation equipment test

system can be more accurate to measurement the

navigation equipment signal, obtain more accurate

measurement results. At the same time, this paper

also proposes an online diagnosis method and

system for navigation equipment. Based on the

accurate measurement results obtained by the above

navigation signal measurement method and system,

the online diagnosis of navigation equipment can be

realized with high accuracy.

Taking the Localizer beacon (belongs to the

Instrument Landing System, ILS) as an example, the

Localizer signal is composed of 90Hz, 150Hz and

1020Hz modulated signals. When analysing the

measurement results of the Localizer signal, it is

necessary to analyse the frequency, amplitude and

phase of 90Hz, 150Hz and 1020Hz signals, and the

Morse code decoded by the 1020Hz signal.

2.1 A Method for Measuring

Navigation Signals

When spectrum analysing the navigation signals,

there are errors usually in the frequency, amplitude

and phase, the all-phase FFT (Fast Fourier

Transformation) spectrum analysis can eliminate or

greatly reduce these errors, so as to improve the

analysis accuracy. FFT panoramic spectrum can be

acquired by performing FFT of different lengths or

two successive segments on the navigation signals

transmitted by the navigation equipment, so as to get

accurate phase by correction. All-phase FFT

spectrum analysis mainly includes two parts: all-

phase data pre-processing and FFT (

M. Nowaczyk, G.

Sek, J. Misiewicz, et al, 2000

When the number of FFT calculation points is N,

the length of data to be processed should be (2N-

1).According to the superposition principle of linear

time-invariant system, the superposition of the

response values generated by all input sequences

should be equal to the response values generated by

the superposition of all input sequences and the

excitation of the system. Using this property, the

data sequences with input system length of (2N-1)

are periodic extended, summed and truncated by the

all-phase data pre-processing, and all the segments

of length N containing input sample point x (n) are

considered. For example, when N=3, the flow chart

is shown in Fig. 1.



 1



(2)w

(1)w

(0)w

(1)w 

(2)w



(2)

(1)

(0)

(1)x 

(2)x 

(0)Y

(1)Y

(2)Y

Figure 1. Flow diagram of all-phase FFT spectrum

analysis.

This method has phase ergodicity because it

considers all the data segmentation cases, thus

weakening the amplitude jump of waveform head

and tail, and improving the signal performance. The

whole process of all-phase FFT can be completed

through the data pre-processed with all phase and

Measurement Method and System for Navigation Signal and Online Diagnosis Method and System for Navigation Equipment

275

the traditional windowed FFT calculation, and the

phase of 90Hz/150Hz/1020Hz signals can be

accurately obtained from the phase spectrum of all-

phase FFT.

DFT (Discrete Fourier Transformation) is used to

calculate the part to be refined to obtain the

frequency spectrum with extremely high precision,

and then the frequency and amplitude are corrected,

which has the advantages of good adaptability and

high precision (

G. H. Hostetter, 1980).

First, the integral of the continuous Fourier

transform changed into three steps: sum the

discretization in time domain and the truncation in

time domain of finite length, are transformed into

the special Fourier transform form of time

discretization and frequency continuity, as follows:

() ()exp 2

Xf xn j n

















0,1,... 1nN

(1)

Where,

00 0

() cos(2 / )xn A f n N









is a

single harmonic signal sequence, whose frequency,

amplitude and initial phase is respectively refer to

A and







is the normalized

frequencies according to frequency resolution

fN . N is the number of FFT points, and

N is the sampling frequency.

Then, refine a specified frequency interval





, set the refinement multiple as D, and the

frequency resolution after refinement is

fD

(2)

Thus, it can be known that the refined

computational frequency sequence is





11 1 2

, , 2 ,...,

fff f f  

(3)

Finally, formula (1) is used to obtain the

amplitude spectrum and phase spectrum of the

frequency sequence to be calculated. The frequency

value corresponding to the maximum point of the

searching amplitude in each refined spectral line is

the estimated frequency of the harmonic signal. The

estimated frequency is searched for frequencies

close to 90Hz/150Hz/1020Hz, and the

corresponding amplitude is obtained by combining

with the phase spectrum of all-phase FFT.

The all-phase FFT spectrum analysis method is

used to analyze the spectrum of the navigation signal

transmitted by the navigation equipment and obtain

the panoramic spectrum. The phases of 90Hz, 150Hz

and 1020Hz signals are determined according to the

panoramic spectrum. The DFT spectrum analysis

method is used to analyze the local part of the

panoramic spectrum and refine the spectrum. The

amplitudes of 90Hz/150Hz/1020Hz signals were

determined according to the refined spectrum.

Navigation signals were measured according to the

phase and amplitude values of 90Hz/150Hz/1020Hz

signals, and the measurement results were obtained.

The measurement results include: 90Hz/150Hz

modulation depth, difference between their

modulation depth, their DDM (Difference in Depth

of Modulation) value, SDM (Sum of the Depths of

Modulation) value, and the Morse code decoded

from the 1020Hz signal. The all-phase FFT

spectrum analysis method is adopted to analyze the

spectrum of the navigation signal transmitted by the

navigation equipment and obtain the panoramic

spectrum, including: the all-phase data

preprocessing method is adopted to preprocess the

navigation signal transmitted by the navigation

equipment. The windowed FFT is applied to the

preprocessed data to obtain the panoramic spectrum.

2.2 A System for Measuring Navigation

Signals

According to the above navigation signal

measurement methods, this paper proposes a

navigation signal measurement system, which

mainly includes: the all-phase FFT module, which is

used to analyse the spectrum of the navigation signal

transmitted by the navigation equipment by using

the all-phase FFT spectrum analysis method, to

obtain the panoramic spectrum. The signal phase

determination module is used to determine the phase

of 90Hz/150Hz/1020Hz signals according to the

panoramic spectrum. The DFT module is used to

analyse the local part of the panoramic spectrum by

using the DFT spectrum analysis method and obtain

the refined spectrum. The signal amplitude

determination module is used to determine the

amplitude of 90Hz, 150Hz and 1020Hz signals

according to the refined spectrum. The signal

measurement module is used to measure the

navigation signal according to the phase and

amplitude values of 90Hz/50Hz/1020Hz signals and

obtain the measurement results.

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

276

Among them, the all-phase FFT module includes:

all- phase pre-processing unit, which is used to pre-

processing the navigation signal transmitted by the

navigation equipment by using the all-phase data

pre-processing method. The windowed FFT unit is

used for windowed FFT after pre-processed data, to

obtain panoramic spectrum.

2.3 An Online Diagnosis Method for

Navigation Equipment

Analysing the impact of changed space of navigation

signal on the measurement results, which is caused

by the surrounding environment, according to the

model of navigation equipment, uses the Method of

Moment (MoM) to draw navigation signal direction,

combines with the conditions of the navigation

equipment’s surrounding terrain or obstacles, uses

the Physical Optics (PO) method to simulate draw a

theoretical course structure, and comparing it with

the true course structure that is draw with the

measurement result by the proposed navigation

equipment online measuring system, if their

structure has similar trend, it shows that the changed

space navigation signal caused by the environment

around the navigation station will affect the

measurement results. If their structural trends are not

similar, it is considered that the navigation

equipment is broken.

When analysing the interference effect of active

radiation near the navigation equipment stations on

ILS/VOR’s space signal measurement, the

electromagnetic propagation theory can be combined

with navigation equipment models, active radiation

near navigation station, to draw a theory of course

structure, and then compare it with the true course

structure that is draw with the measurement result, if

the trend of their structure are similar, it shows that

the active radiation near the navigation station will

affect the measurement results. If their structural

trends are not similar, it is considered that the

navigation equipment is broken.

Finally, the equipment status diagnosis can be

established to provide reference for the preventive

and corrective maintenance of navigation equipment,

based on the above results. Combined with the

active or passive interference around the navigation

equipment station, this paper analyses whether the

measured data (e.g. DDM) measured in and around

the airport runway is similar to the structural trend of

the simulated course structure or not. If not, the fault

of the navigation equipment can be determined.

2.4 An Online Diagnosis System for

Navigation Equipment

The online diagnosis system of navigation

equipment includes: navigation signal measurement

module, which is used to measure the navigation

signal transmitted by the navigation equipment with

the navigation signal measurement method provided

in this paper, to eliminate or reduce the interference

of environmental factors on the measurement, and

obtain the measurement results. The actual

navigation structure drawing module is used to draw

the actual navigation structure according to the

measurement results. The simulation navigation

structure drawing module is used to draw the

theoretical simulation navigation structure according

to the model of the navigation equipment. The

navigation structure comparison module is used to

judge whether the structure trend of the actual

navigation structure and the simulated navigation

structure is similar or not. Navigation fault

determination module is used to judge the failure of

navigation equipment.

3 SPECIFIC IMPLEMENTATION

MODE

The navigation signal measurement method

provided in this paper includes the following steps:

Step 1: the all-phase FFT spectrum analysis method

is adopted to analyse the spectrum of the navigation

signal transmitted by the navigation equipment, and

obtain the panoramic spectrum.

Step 2: determine the phase of 90Hz/150Hz/ 1020Hz

signals according to the panoramic spectrum.

Step 3: the Discrete Fourier Transform spectrum

analysis method is adopted to analyse the local

spectrum of the panoramic spectrum, and obtain the

refined spectrum.

Step 4: determine the amplitude of 90Hz, 150Hz and

1020Hz signals according to the refined spectrum.

Step 5: measure and obtain the navigation signal

according to the phase and amplitude values of 90Hz,

150Hz and 1020Hz signals.

The measured results include the modulation

value of 90Hz and 150 Hz signal, and their DDM

and SDM value, and Morse code.

In this paper, the navigation signal measurement

method adopts the combination of all-phase FFT

spectrum analysis method and DFT spectrum

analysis method for spectrum analysing, eliminates

or substantially reduces the interference of

Measurement Method and System for Navigation Signal and Online Diagnosis Method and System for Navigation Equipment

277

environmental factors on navigation signals, and

obtains accurate measurement results. Based on the

above navigation signal measurement method, this

paper proposes an online diagnosis method for

navigation equipment, which includes the followings:

Step 1: measuring the navigation signal

transmitted by the navigation equipment with the

navigation signal measurement method provided in

this paper, so as to eliminate or reduce the

interference of environmental factors on the

measurement, and obtaining the measurement results.

Step 2: drawing the actual navigation structure

diagram according to the measurement results.

Step 3: drawing the theoretical simulated

navigation structure diagram according to the model

of the navigation equipment, including: according to

the model of the navigation equipment, drawing the

direction diagram of the navigation signal using the

moment method. According to the terrain and

obstacles around the navigation equipment, and the

direction diagram of the navigation signal, drawing

the theoretical simulated navigation structure

diagram with the physical optical method.

According to the model of navigation equipment and

the active radiation situation near the navigation

station, a theoretical simulated navigation structure

diagram is drawn based on the electromagnetic

propagation theory.

Step 4: judging whether the structure trend of the

actual navigation structure diagram and the

simulated navigation structure diagram is similar.

Determining the factors that cause interference to the

propagation of navigation signals according to the

drawing method adopted to draw the simulated

navigation structure diagram. If they are not similar,

it shows that the navigation device has a fault.

Combining with the active or passive

interference around the navigation equipment station,

the paper analyses whether the measured data

measured in and around the airport runway is similar

to the simulated course structure’s trend. If not, the

fault of the navigation equipment can be determined.

4 CONCLUSIONS

In this paper, a navigation signal measurement

method is proposed, which combines the all-phase

FFT spectrum analysis method and DFT spectrum

analysis method for spectrum analysing, to eliminate

or substantially reduce the interference of

environmental factors on navigation signals, and

then obtain accurate measurement results.

In addition, this paper proposes an online

diagnosis method for navigation equipment. Firstly,

the navigation signal measurement method is used to

measure the navigation signal transmitted by the

navigation equipment, to eliminate or reduce the

interference of environmental factors on the

measurement, and obtain the measurement results.

Afterwards, draw the actual navigation structure

chart according to the measurement results. Thirdly,

draw the theoretical simulation navigation structure

diagram, according to the model of the navigation

equipment. Finally, determine whether the structure

trend of the actual navigation structure chart is

similar to that of the simulated navigation structure

chart, if they are not close, the navigation device is

judged to be faulty.

In this paper, based on the navigation signal

measurement method and its accurate measurement

results, drawing the actual navigation structure

diagram and comparing it with the theoretical

navigation structure diagram, the online diagnosis of

navigation equipment can be realized according to

the comparison results, with high accuracy.

Analysing the influence of passive and active

interference on navigation equipment, this paper

provides more accurate judgment basis for the

analysis of measurement results. Through the

calibration error, relatively certain measurement

results are obtained.

ACKNOWLEDGEMENTS

This paper is supported by the East China Air

Traffic Management Bureau CAAC‘s Science and

Technology Project Plan (CS20180831-54#), and

the National Key R&D Program of China

(2017YFB0503402). The authors would like to

thank the anonymous reviewers and editors for their

helpful comments and suggestions.

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